Mechanistic Toxicity Assessment of Nanomaterials by Whole-Cell-Array Stress Genes Expression Analysis

Abstract

This study performed mechanistic toxicity assessment of nanosilver (nAg) and nanotitanium dioxide anatase (nTiO2_a) via toxicogenomic approach, employing a whole-cell-array library consisting of 91 recombinated Escherichia coli K12 strains with transcriptional GFP-fusions covering most known stress response genes. The results, for the first time, revealed more detailed transcriptional information on the toxic mechanism of nAg and nTiO2_a, and led to a better understanding of the mode of action (MOA) of metal and metal oxide nanomaterials (NMs). The detailed pathways network established for the oxidative stress system and for the SOS (DNA damage) repair system based on the temporal gene expression profiling data revealed the relationships and sequences of key genes involved in these toxin response systems. Both NMs were found to cause oxidative stress as well as cell membrane and transportation damage. Genotoxicity and DNA damage were also observed, although nTiO2_a induced SOS response via previously identified pathway and nAg seemed to induce DNA repair via a pathway different from SOS. We observed that the NMs at lower concentration tend to induce more chemical-specific toxicity response, while at higher concentrations, more general global stress response dominates. The information-rich real-time gene expression data allowed for identification of potential biomarkers that can be employed for specific toxin detection and biosensor developments. The concentration-dependent gene expression response led to the determination of the No Observed Transcriptional Effect Level (NOTEL) values, which can be potentially applied in the regulatory and risk assessment framework as an alternative toxicity assessment end point.

Improved Acetic Acid Resistance in Saccharomyces cerevisiae by Overexpression of the WHI2 Gene Identified through Inverse Metabolic Engineering

“…The protein expression levels based on GFP signals were calculated using the method previously described (39,40). The raw data from the OD 600 and GFP measurements were corrected by considering the background signals in control with medium only, and the protein expression per cell unit for each measurement was calculated by normalizing the GFP data to the cell number (OD 600 ), with P equal to the GFP measurement over the OD 600 .…”

Analysis of engineered nanomaterials in complex matrices (environment and biota): General considerations and conceptual case studies

“…For example, enzyme-linked immunosorbent assays, which use specific antibodies and enzymes, have been widely used for the low-level analysis of molecules. The specific association of AgNPs with cell surface proteins [12] and the differential expression of bacterial stress response genes with AgNPs and TiO 2 nanoparticles [13] indicate that biological reporter systems [14] that are highly specific to nanoparticle surfaces could be developed. Biosensors are very sensitive and, because they report on interactions of nanoparticles with living systems [15,16], should provide assessments of bioavailable fractions of nanoparticles, which are highly relevant to understanding exposure.…”

Identification of Soil Bacteria Susceptible to TiO 2 and ZnO Nanoparticles

“…Pure culture studies regularly report both acute toxicity and sublethal effects of ENPs on bacteria through mechanisms including membrane disorganization, DNA damage, surface-coating-related photocatalytic oxidation, and reactive oxygen species (ROS) production (5,10,23,44). This suggests that ENPs could be toxins when released into soil, e.g., harming or killing microorganisms.…”

“…Previous studies also demonstrated distinct effects of nano-TiO 2 on phyllosphere microbial communities (51), activated sludge bacterial communities (56), and microbial biofilms in stream microcosms (3), which partially support our observations in the terrestrial system studied here. The potential mechanism could be the direct toxicity of ENPs on soil bacteria through the release of metal ions or attachment-related cell damage (5,10,23,28,44). ENPs may also indirectly affect soil bacteria by changing nutrient availability or the bioavailability of cooccurring contaminants and by changing physical properties of the soil due to their large surface area and high reactivity (4,25).…”